Not sure what a lame error 47 is, but it's possible to go below 32000Hz. From the lame documentation: ======================================================================= LOW BITRATES ======================================================================= At lower bitrates, (like 24 kbps per channel), it is recommended that you use a 16 kHz sampling rate combined with lowpass filtering. LAME, as well as commercial encoders (FhG, Xing) will do this automatically. However, if you feel there is too much (or not enough) lowpass filtering, you may need to try different values of the lowpass cutoff and passband width (--resample, --lowpass and --lowpass-width options). Are you using the latest version of besweet? You might also just try LAME alone with a wav input. Could be a besweet handling bug.